1. Field of the Invention
The present invention relates to a dot matrix line printer, and more particularly, to a line printer to which a pulse excitation is applied and a printing head is scanned horizontally to print with a high speed and an enhanced efficiency and the noise and vibration thereof is absorbed.
2. Description of the Related Art
Wire-dot line printers are widely utilized in the field of data-processing devices, computers or telecommunication utilities. In this type of printer, a plurality of wire-dot printing heads are mounted to a shuttle at an appropriate distance, and the shuttle is moved at regular intervals of the head and the printer prints out Chinese characters or other characters for a plurality of lines at one time. When a printing of one dot line is completed, a print paper is fed for a single line spacing, the movement of the shuttle is reversed to print the next line, and thus by repeating such operation, lines can be printed one-by-one. Accordingly, a drive unit is provided in the shuttle to cause a reciprocal motion of the shuttle.
In the known prior art a shuttle drive unit for the above-described line printer is constituted by a direct-current linear motor arranged in the shuttle as a driving means and a drive signal is input to the linear motor from the driver unit to drive the linear motor. Further, the driver control means is formed by microprocessors to control the driver unit. A sensor is provided for detecting the position of the shuttle in the printer, which feeds back the position signal to control the driver control means.
The above-described driver control means controls the driver unit to enable the shuttle to implement the following two operations. That is, first, the operation of the shuttle while the line printer is printing; i.e., the shuttle is made to travel at a constant velocity in two directions, and, second, the motion of the shuttle from one print position to the following print position; that is, a reversal of the motion, is carried out during a time interval of from the time when the constant speed travel in one direction is finished, to the time when the next constant speed travel is commenced.
This control causes a drive signal to be output from the driver to a linear motor of the shuttle and printing by the printer is enabled by the reciprocal motion of the shuttle.
The printer conventionally carries out the printing in accordance with information transferred from a host computer. Thus, the printer can execute printing for one line only when at least one line of printing information is stored in a buffer memory of the printer. Therefore, if the timing when one line of printing information stored in the buffer is completed coincides with the timing of the reciprocal movement of the shuttle, the shuttle can implement printing by a forward movement and a backward movement.
When these timings deviate from the normal routine, due to circumstances beyond control, printing can not be implemented even if the shuttle is in motion. That is, even when the shuttle starts to travel, if one line of printing information is not yet stored, storing of the printing information in the printer is completed during the travel of the shuttle motor unit. As a result, printing of that information can not be implemented during the travel of the shuttle and during the next travel of the shuttle, the printing based on the printing information is implemented, and under these circumstances the overall printing speed is reduced.
Further, when printing is implemented by a printer, sometimes a comparatively longer paper feed time is necessary, and in this case, an unnecessary printing of dot lines by the reciprocal movement of the shuttle is carried out.